Anyone who has ever wished they were an actor, a detective, an undercover agent, an investigative reporter or a global traveller would fit in perfectly at the Environmental Investigation Agency (EIA).

Campaigners at the charity spend as much as six months each year working undercover all over the world to expose environmental crimes from the sale of tiger-skins in China to illegal logging in Indonesia to ivory trading in Malawi. In stark contrast to the big conservation charities like Greenpeace and the WWF, the EIA's 20 staff work in an office above Café Uno on London's Upper Street, Islington, and there is barely any money for marketing. Yet, for a tiny charity, it packs an almighty punch. Since it was launched in 1984, the team has fought dozens of global environmental battles, from playing an instrumental part in the banning of the ivory trade in the late 80s to helping stamp out the illegal sale of ozone-destroying CFC chemicals in the US in the 90s.

"We're small, but we have a niche, and that is an investigative approach, regarding these issues as crimes," says campaigns director and ex-journalist Julian Newman. "My interest is about justice - organised criminal gangs looting the planet for their own profit and nobody really doing anything about it."

The EIA was set up by people who had worked for big conservation charities, and felt there was a need for a more flexible, fast-moving operation, which could get evidence of environmental offences by working undercover on the ground, and then lobby governments for change.

"Our philosophy is to get close to these issues and not just sit at a desk in London writing reports based on other people's reports," says Newman. "Actually going out into the field and documenting how these crimes are being committed gives us a strong voice in negotiations."

Eyes and earsWith all the environmental problems in the world, the EIA focuses on crimes other organisations are not investigating, which it hears about through a global network of informers as well as its own research. A vast atlas takes pride of place in the office's meeting room, and a dedicated editing suite is crammed from floor to ceiling with hundreds of tapes of undercover footage.

Typically, a group of two or three campaigners will spend up to six months briefing themselves for undercover missions. "It takes a lot of preparation to be get close to targets and be convincing in your role," says Newman.

Staff are trained with specialist skills such as how to analyse wildlife specimens, tell the difference between real and fake skins at a second's glance and use specialist industry terminology. Campaigners then work for several weeks or months in the field, wearing secret cameras and microphones to get the evidence they need to build convincing cases.

They become consummate actors, posing, for instance, as Western investors, timber traders or chemicals dealers, using carefully-crafted aliases and carrying phoney business cards representing dummy companies. Every member of this not-for-profit group is passionate about their work - and they have to be, given the dangers of working undercover. Although EIA has stringent safety measures in place, campaigners' work is often nerve-wracking. Only once in the last 10 years has an investigation gone wrong, when two EIA staff were discovered filming illegal logging in an Indonesian forest by the company under investigation. They were held in a room, beaten up - one lost a finger - and threatened with a gun before escaping.

Funding sourcesThe EIA's trips, governmental lobbying and training of local investigative partners are funded by a small, loyal membership and grants from foundations and the Department for International Development (DfID). "We never have enough money but we do use our money very well," says Newman.

Deborah Banks, head of EIA's tiger campaign, believes that being a small not-for-profit organisation is an advantage.

"The one thing that keeps me here is our size," she stresses. 'We don't have layers and layers of bureaucracy; we can change plans. There's a tenacity about the organisation."

In the offices of other, larger environmental charities, the sofa in reception might be covered with neat cushions - at the EIA, it has been turned into a makeshift bed for a sleepy campaigner who has just flown in from the US. There is no faceless corporate red tape here, just a commitment to justice.